Importance of filament reactivity for CVD diamond growth

The behavior of tungsten filaments heated up to 2500 degrees C in mixtures of CH4 or C2H2 and H2 at P = 9 and 25 Torr is analyzed. It has been found that the filament resistance R, spectral emissivity ε, power consumption, and CH4 and C2H2 partial pressures depend critically on the filament temperature as well as the reactant CH4/H2 or C2H2/H2 traction. The authors interpret these results on the basis of a thermodynamic model which predicts that transitions between deposition and etching of solid carbon occur on the filament surface at high temperatures. The implications of these results for diamond CVD are discussed. Evidence for gas phase reactions is also presented